This invention relates to radiography and more particularly is to a scanning X-ray system and method for simultaneously producing a plurality of radiographic images from a single scanning X-ray exposure of the subject in which the several images exhibit widely varying contrast range characteristics to emphasize different aspects of the same region of the subject.
Conventional X-ray imaging systems in which the subject is situated between a fixed point X-ray source and a photographic film or fluorescent screen, are undersirably limited in the range of contrast obtainable in the image produced by a single exposure of the subject to X-rays. In the absence of the apparatus and techniques to be hereafter described, this is also true of a scanning X-ray system in which the subject is situated between a point source of X-rays which sweeps through a raster pattern while a relatively small area X-ray detector controls light intensity at the screen of an oscilloscope undergoing a similar raster pattern to generate a radiographic image at the screen of the oscilloscope. While oscilloscopes customarily have contrast and brightness controls, these must be set at some particular value during a single exposure of the subject. If these values are set to emphasize slight differences of X-ray absorbancies in the scanned area of the subject, such as differences between a tumor and healthy tissue in a medical patient, then other areas of widely differing X-ray absorbancy such as bony structures and adjacent soft tissue are obscured in the image. If controls are set to contrast areas of the subject of widely different X-ray absorbancy, then the areas of slight difference are obscured.
In general, most X-ray imaging systems are limited in their dynamic range of contrast to one or two orders of magnitude. Repeated exposures of the subject must be made to obtain desired information in many cases. In the case of the scanning system, as briefly described above, this does not result from any lack of information content in the signals produced by the X-ray detector in the course of a single scan of the subject, but instead derives from the limitations in the associated signal processing and display means, including the limited gray scale range of the oscilloscope screen and the limited contrast capabilities of photographic film which may be used to photograph the display on the oscilloscope screen.